Yeah it seemed odd that it was a PON LED that was showing the error and not the LOS, sounds like it just gave up the ghost and didn't like the OLT haha.

All stable and working now - TTB gave me a call this afternoon to check if all was well, so i'm pretty impressed on how quick this got resolved!

Who knows it may have been kicking around (quite literally) with the builders /developers or otherwise not had a kind existence before you had it livened up. Then it just died.